Method and a device for intervention in an underwater production well

ABSTRACT

A method for intervention in an underwater production well, in which the well head ( 1 ) of the production well is located on the seabed ( 2 ), and wherein a drilling rig ( 26 ), which comprises at least a robotized drill floor ( 32 ), is placed at the well head ( 1 ), after which necessary intervention operations are carried out in a remote-controlled manner by means of the drilling rig ( 26 ).

This invention relates to a method for intervention in an underwater production well. More particularly, it relates to a method for intervention in an underwater production well, in which the well head of the production well is located on the seabed, and wherein a drilling rig, which comprises at least a robotized drill floor, is placed at the well head, after which necessary intervention operations are carried out in a remote-controlled manner by means of the drilling rig. The invention also comprises a device for practising the invention.

In this connection, intervention and intervention operations imply repair- and maintenance operations in a well, typically a producing petroleum well, requiring tools to be moved into the well. The term drill floor is used in the sense of an area from which intervention operations are carried out, and it also comprises necessary equipment normally located on a drill floor.

A considerable number of underwater production wells exist, in which the well head of the well is located on the seabed.

The fluid being produced from the well flows from the well and into pipes connected to the well head of the well.

From time to time, it is necessary to carry out intervention operations in order to, among other things, maintain components in the well, or to shut off or open sections of the producing formation.

According to prior art, a blowout preventer is connected to the well head when intervention operations are to be carried out, after which a marine riser, which belongs to an intervention vessel located at sea level, is connected to the blowout preventer. Then, intervention operations are carried out by means of a workover riser, which is also connected to the blowout preventer, and which is provided with necessary valves at the surface.

Operations of this type are weather-dependent, and it is not uncommon to have to discontinue intervention operations due to bad weather. When the operation is discontinued, the marine riser and the workover riser must be disconnected from the blowout preventer on the seabed and reconnected when the intervention operation is to be resumed. It is evident that interruptions in the intervention operation may increase costs and prolong well maintenance operations significantly.

The object of the invention is to remedy or reduce at least one of the disadvantages of the prior art.

The object is achieved in accordance with the invention and by virtue of the features disclosed in the following description and in the subsequent claims.

A method according to the invention for intervention in an underwater production well, in which the well head of the well is located on the seabed, is characterized in that a drilling rig, which comprises at least a robotized drill floor, is placed at the well head, after which necessary intervention operations are carried out in a remote-controlled manner by means of the drilling rig.

Advantageously, the drilling rig, which is submerged, is connected to a bottom frame, which fits in a complementary manner to the well head, is first lowered and anchored to the seabed. A blowout preventer, a so-called BOP, is connected to the well head.

The anchoring of the bottom frame to the seabed may be carried out by means of at least one suction anchor. In this connection, suction anchors exhibit several favourable features. Suction anchors may be displaced into the seabed without risking damage to the well or the well head. It is relatively simple to displace suction anchors into the ground to the desired depth so as to allow the bottom frame to correspond, in terms of height, to that of the well head. Further, suction anchors may be released relatively simply from the sea floor. The bottom frame may be guided down in a manner known per se by means of two or several guide wires.

Advantageously, a support frame is mounted on the bottom frame when the drilling rig is mounted on the support frame. Thereby, the drilling rig is connected to the bottom frame by means of the support frame. The bottom frame may be erected to the height of an upper portion of the well head. Thereby, the support frame, which extends upwards from the bottom frame, will surround the blowout preventer of the well.

Thus, the bottom frame, which fits in a complementary manner to the well head, and which is anchored to the seabed, preferably by means of at least one suction anchor, forms a base for the drilling rig.

Document NO 20053279 describes a drilling rig placed on the seabed. The drilling rig corresponding to NO 20053279 may be formed as an intervention drilling rig and mounted on the support frame. Reference is made to NO 20053279 for description of the manner of operation of the drilling rig with respect to the supply of materials and operation of the drilling rig.

Advantageously, the drilling rig is provided with a drilling module having pipes supplied thereto from a drill pipe magazine. Normally, the drilling rig is also provided with necessary pumping- and cleaning equipment for drilling fluid.

The drilling rig may comprise necessary equipment for at least coiled-tubing or wireline operations.

A method and a device according to the invention, in which a drilling rig is placed on the seabed at the well head of the well, renders possible for intervention operations to be carried out substantially independent of the weather, simultaneously substantially obviating problems related to the mechanical connection of a weather-affected vessel to a well head on the seabed.

In the following, an example of a preferred method and embodiment is described and depicted in the accompanying drawings, in which:

FIG. 1 shows, in perspective, a well head placed on the seabed, and in which a bottom frame is being lowered to the well head;

FIG. 2 shows, in perspective, the well head and the bottom frame after having anchored the well head in the seabed;

FIG. 3 shows, in perspective, the well head and the bottom frame after having mounted a blowout preventer on the well head; and

FIG. 4 shows, in perspective, the well head after having mounted a drilling rig on the bottom frame by means of a support frame.

In the drawings, reference numeral 1 denotes a well head connected to a well (not shown) placed on the seabed 2 and connected to a number of pipe connections 4. A protective frame 6 is placed over the well head. The well head 1 is provided with guide-in columns 8.

In FIG. 1, a bottom frame 10 is shown during lowering to the well head 1. The necessary guide wires and hoisting equipment are not shown. The bottom frame 10 comprises a frame portion 12, which is horizontal in its position of use, provided with eight downwardly projecting leg columns 14. The leg columns 14 are connected each to a respective suction anchor 16. The suction anchors 16 are arranged so as to be able to be displaced down into the seabed 2 in a manner known per se, see FIG. 2.

Four guide mandrels 18 extend upwardly from the frame portion 12, the guide mandrels 18 being distributed around the central axis 20 of the bottom frame 10, the central axis 20 being vertical in its position of use.

Having guided the bottom frame 10 into the desired position relative to the well head 1, and having displaced the suction anchors 16 to the desired depth in the seabed 2, a blowout preventer 22 may be guided down onto the well head 1 and connected to the well head 1 by means of guide wires and guide-in columns 8 (not shown), see FIG. 3.

Alternatively, the blowout preventer 22 may be connected to the well head 1 before mounting the bottom frame 10.

Having anchored the bottom frame 10, a support frame 24 may be guided down onto the guide mandrels 18 of the bottom frame 10 by means of guide wires (not shown), see FIG. 4. The support frame 24 is connected to the bottom frame 10 in a manner known per se, for example by means of hydraulically operated locking connections (not shown).

A drilling rig 26, which is arranged to be controlled from the surface, is then lowered onto the support frame 24 and is connected thereto. The drilling centre 28 of the drilling rig 26 corresponds to the centre 30 of the well head A and the blowout preventer 22.

In this preferred exemplary embodiment, and in addition to a robotized drill floor 32 with a power tong 33 and necessary connections (not shown) to a vessel at the surface, the drilling rig 1 is provided with a drilling module 34, a number of pipe magazines 36 and also a pumping module 38 for drilling fluid and a support module 40 comprising, among other things, cleaning equipment (not shown) for drilling fluid.

In FIG. 4, a tool magazine 42 and a manipulator 44 are shown through openings 46 in walls 46 of the robotized drill floor 32. During operation the openings 46 are closed.

Thus, the drilling rig 26 is arranged so as to be able to carry out, in a remote-controlled manner, relatively heavy intervention operations in the well (not shown). 

1. A method for intervention in an underwater production well, in which a well head of the production well is located on the seabed (2), wherein the method includes: arranging a bottom frame, which fits in an independent and complementary manner to the well head (4) on the sea bed; anchoring the bottom frame to the seabed; arranging a submerged drilling rig, on the bottom frame above the well head after which necessary intervention operations are carried out in a remote-controlled manner by means of the drilling rig.
 2. The method in accordance with claim 1, wherein the method includes arranging a robotized drill floor in the drilling rig.
 3. The method in accordance with claim 2, wherein the method includes arranging a support frame between the bottom frame and the drilling rig.
 4. An equipment device for intervention in an underwater production well, in which a well head of the production well is located on the seabed, wherein the equipment comprises a bottom frame, which fits in a independent and complementary manner to the well head, and where the bottom frame is anchored to the seabed and forms a base for a submerged drilling rig.
 5. The equipment device in accordance with claim 4, wherein the submerged drilling rig is located at the well head, and where the drilling rig includes a robotized drill floor.
 6. The device in accordance with claim 4, wherein the drilling rig is connected to the bottom frame by means of a support frame.
 7. The device in accordance with claim 6, wherein the support frame surrounds a blowout preventer for the well.
 8. The device in accordance with claim 4, wherein the drilling rig is provided with a drilling module.
 9. The device in accordance with claim 4, wherein the drilling rig is provided with a drill pipe magazine. 